Disentangling interfacial and alloying effects in bimetallic PtCr- reverse water gas shift catalysts

Promotional effects are ubiquitous across catalytic processes involving supported nanoparticles, where additional elements – so-called promoters – enhance significantly the catalytic performances (activity, selectivity and stability) of nanoparticles. However, the inherent complexity of these catalysts makes it difficult to underline the effect of promoters at the molecular level. Surface organometallic chemistry (SOMC) is a powerful tool to decouple the complexity of catalysts by constructing better-defined model systems. In this study, we compare two SOMC approaches to construct PtCr bimetallic catalysts with or without Cr interfacial Lewis acid sites for the low-temperature reverse water-gas shift (RWGS) reaction. Notably, we show that a catalyst containing exclusively PtCr alloys, PtCr@SiO2, displays a substantial promotional effect in catalytic activity compared to monometallic Pt@SiO2, while having additional Cr-interfacial sites (PtCr-Crint@SiO2) further improves the catalytic activity. In situ spectroscopic results reveal that PtCr alloy facilitates a redox reaction pathway, whereas an additional formate-mediated pathway takes place at the interface between PtCr alloy and Cr(III) Lewis acid sites. These findings highlight that both PtCr alloy and Cr-interfacial sites contribute to enhancing the RWGS activity. The insights gained from these well-defined systems provide guidelines for the rational design of more active catalysts.